Oblique Crossover Crunches :-

        Lie on your back and cross right foot over left knee.  Lift shoulder blades off the floor and curl left shoulder towards right knee, contracting the right side of waist.   Lower and repeat on the same side before switching sides.

Bicycle Exercise for Abs :-
      The Bicycle exercise is the best move to target the rectus abdominis (i.e., the 'six pack') and the obliques (the waist), according to a study done by the American Council on Exercise. To do this exercise correctly:
            1. Lie face up on the floor and lace your fingers behind your head.
            2. Bring the knees in towards the chest and lift the shoulder blades off the ground without pulling on the neck.
            3. Straight the left leg out to about a 45-degree angle while simultaneously turning the upper body to the right, bringing the left elbow towards the right knee.
            4. Switch sides, bringing the right elbow towards the left knee.
            5. Continue alternating sides in a 'pedaling' motion for 12-16 reps.

Captain’s Chair :-
      The Captain’s Chair is the second most effective move for the rectus abdominis as well as the obliques and can be found in most health clubs and gyms. To do it right:
          1. Stand on chair and grip handholds to stabilize your upper body.
          2. Press your back against the pad and contract the abs to raise the legs and lift knees towards your chest.
          3. Don't arch the back and remember to breathe smoothly.
          4. Slowly lower back down and repeat for 12-16 reps.